Dorothy Height, a leading civil rights pioneer of the 1960s, died Tuesday at age 98, Howard University Hospital confirmed.

Height died at 3:41 a.m., said hospital spokesman Ron Harris. No cause of death was given.

Height, who had been chair and president emerita of the National Council of Negro Women, worked in the 1960s alongside civil rights pioneers, including the Rev. Martin Luther King Jr., future U.S. Rep. John Lewis and A. Philip Randolph. She was on the platform when King delivered his “I Have a Dream” speech at the 1963 March on Washington.

President Obama called her a hero, saying she “served as the only woman at the highest level of the civil rights movement — witnessing every march and milestone along the way.”